Muscular Dystrophy
- Inherited
progressive degenerations of muscle
- differentiate
from polymyositis, which has more rapid course with higher CK levels, more
fibrillation, and responsiveness to steroids
- All
produce Elevations of serum CPK and aldolase with myopathic pattern on EMG;
diagnosed by muscle biopsy
- Congenital
muscular dystrophy – more common in Japan, autosomal recessive
- Duchenne’s
disease – most
common muscular dystrophy
- X-linked
recessive (but 1/3 are spontaneous), M>F
- Affects
1/3500 births; become symptomatic at 2-5 yrs, 75% dead by 25 years
- Symmetrical
relentlessly progressive weakness
- Decreased
dystophin in muscle fibers (stabilizes membranes) – see muscle fiber
necrosis/regeneration
- Atrophy
worse in shoulder and pelvic girdle; calf seems to hypertrophy
- Spares
hands/face/eyes
- Associated
with mental retardation, CHF, and respiratory problems
- Prognosis:
survival beyond age 25 is rare
- Becker’s
disease –
milder form of Duchenne’s
- X-linked
recessive, M>F
- Affects
1/30,000 births; becomes symptomatic at 11 years, nonambulatory by 30
years, most dead by 50 years
- Dystrophin
abnormal – no necrosis/regeneration
- Less
severe than Duchenne’s, with slower course and later age of onset
- Fascioscapularhumoral
dystrophy
- Slowly
progressive mild weakness involving face, shoulder girdle and proximal
arm with onset in 3rd and 4th decades
- Autosomal
dominant on chromosome 4, variable penetrance
- Symptomatic
10-20 years
- Face
affected first, then shoulders and upper arm
- Associated
with sensorineural hearing loss
- Chronic
inflammatory cells seen in muscle (only MD to do this)
- CK
normal; no associated CHF or mental retardation
- Sometimes
associated with absence of a muscle
- Limb-Girdle
Syndrome
- Autosomal
recessive
- Axial
weakness
- Sometimes
associated with CHF, no mental retardation
- 1/3 have
pseudohypertrophy
- Oculopharyngeal
muscular dystrophy
- Autosomal
dominant
- Becomes
symptomatic 40-50 years
- Weakness
of eye muscles and pharynx
- Myotonic
Dystrophy –
most common muscular dystrophy in adults
- Slowly
progressive weakness involving face, neck and distal extremities with
onset in 2nd and 3rd decades
- Autosomal
dominant on chromosome 19 with variable penetrance
- Affects
1/20,000 births; generally nonambulatory 20 years after first symptoms
- Face
affected first, then distal extremities
- Weakness
and myotonus (cannot relax muscle after contraction)
- Dysrhythmia
(especially with quinine, procainamide, and phenytoin which increase AV
block), decreased intelligence, cataracts, endocrine dysfunction,
testicular atrophy, frontal balding